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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

94                                  ALASKAN GLACIER STUDIES
summarizes the main results of the earlier observations down to the close of 1906, and has been freely paraphrased here,1 with minor additions. Turner Glacier flows from an unknown source upon the slopes of Mt. Cook through a valley nearly a mile wide and with walls five to six thousand feet high (PI. XXXVII). Its visible slope is moderate and fairly regular, and the rapidly-moving ice is severely crevassed. Where the glacier passes from its mountain valley into Disenchantment Bay it expands to two miles in width (Map 3) and the slope is steepened from less than ten to as much as twenty-five degrees, a change which Gilbert correctly interpreted as indicating the hanging, valley condition,, due to the overdeepening of the main fiord by the larger, expanded Hubbard Glacier at the time when the smaller Turner Glacier was its tributary. The floor of this valley probably hangs well above the fiord bottom, and perhaps lies even above present water surface. Hah8 a mile back from the terminus, and about half way between the medial and south lateral moraine, there was, in 1906, a massively-crevassed bulge, or dome, suggesting an unexposed nunatak and indicating that the ice was not very thick. Below the steep slope the ice expands into a flat-topped fan or bulb terminated by a crevassed cliff 200 to 220 feet or more high, whose height is shown specifically in PI. XXXVin, where it is compared with a New York office building, drawn carefully to the same scale. The levelness of this ice foot suggests that it is either afloat, as Gilbert thought, or else resting on a flat rock surface. If afloat Gilbert estimates that there must be 1500 to 1600 feet of water here, but soundings are not available for determining this. It does not seem probable, however, that the glacier terminus is actually afloat, for the only known depths nearby are 264 feet just west of Haenke Island, 144 to 282 feet between Turner and Hubbard Glaciers near Osier Island, and 720 feet (no bottom) southwest of Haenke Island. The nearest of these is nearly two miles from Turner Glacier, but the depth of 1500 to 1600 feet is not thought probable, for the greatest depths in all Yakutat Bay are only 1002 to 1119 feet (PI. XCI), and the depth on the side of the bay near the Turner Glacier would normally be considerably less than the maximum. Still another reason for not believing this glacier front to be afloat is the nature of the iceberg discharge. If it were afloat there should be occasional larger masses breaking from the front; but as a matter of fact the icebergs discharged are all of small, or moderate size such as come from the grounded front of a tidal glacier.
The front of Turner Glacier is not a completely-symmetrical bulb or fan, such as forms where glaciers emerge from confining valleys into broader spaces on the land, for iceberg formation and melting in the fiord check complete development of the bulb form. This expanded bulb has, therefore, a truncated terminus with a fairly straight, tidal ice cliff, over two miles long in 1905, flanked by wing-like, moraine-covered points which ended on the land about 2| miles apart. Icebergs are steadily discharged from the cliff and float seaward with those from Hubbard Glacier, ma-Tang an iceberg barrier so hard to penetrate that we found it difficult to work a boat up to within a half mile of the south edge of the glacier in 1905, and quite impossible in a half day's work in 1906.
The lateral moraines of Turner Glacier terminated in the tips of the wing-like edges of the ice front, the one on the south being compound. North of it were two narrow, indistinct, parallel, lateral moraines, then thin, narrow bands of debris, and then a
i Tarr, R. S. and Martin, Lawrence, Glaciers and Glariation of Yakutat Bay, Alaska, Bull. Amer. Geog. Soc., Vol. XXXVJLL1,1906, p. 149. Tarr, R. S., The Yakutat Bay Region, Alaska, Prof. Paper 64, U. S. Geol. Survey, 1909, pp. 89-40.